At the present time, large numbers of electronic timepieces are being produced, in which a quartz crystal vibrator is used in an oscillator circuit to form a standard frequency signal. Such timepieces could initially be categorized into the digital type, in which time data is displayed in digital form by means of an electro-optical display device such as a liquid crystal display, and those having conventional time indicating hands and a dial. The latter type of timepiece is commonly referred to as an "analog" type, although it is of course perfectly possible to provide an analog display of time data by means of a liquid crystal display device. However, for convenience of description, a timepiece time display comprising time indicating hands and a dial will be referred to herein as an analog display. In recent years, a third type of electronic timepiece has come into widespread use, in which an analog display of the type referred to above is combined with a digital display of time. Such timepieces are designed to provide the advantages of an analog display (i.e. easy discrimination of the difference between the current time and some future time, or of the time which has elapsed between some time in the past and the current time), with the advantages of high readout precision, easy provision of a large number of different function modes, display of calendar data, etc.) that are provided by a digital display. However, some difficulties arise with respect to the method of correcting the analog and digital time data displayed by such a timepiece. In a purely analog display electronic timepiece, correction can be easily, conveniently and rapidly performed by means of rotation of an external operating member, i.e. the timepiece crown, in the same way as is done with a conventional mechanical timepiece. This is possible because the timekeeping hands are driven through a gear train by a stepping motor, in such a timepiece. With such a correction system, the correction of minutes and hours is performed in a smooth and continuous manner, i.e. when a time of 59 minutes has been set and the crown is rotated further in one direction, the minutes hand will go to zero and the hours hand will indicate the next hour. If some overshoot occurs during the correction process, past the desired time, then this can easily be remedied by rotating the crown slightly in the opposite direction. With a digital display timepiece, on the other hand, it is generally necessary to depress a pushbutton switch one or more times to set the hours or minutes time data. In other words, if correction of the minutes data has been selected, then each depression of the correction switch pushbutton will result in the minutes being incremented by one. Similarly, if the hours have been selected for correction, each depression will result in an increment of one hour. Thus, when correcting the minutes data, it may be necessary to depress the correction switch up to 59 times. In this case, if the switch is depressed once too often, by mistake, then it will be necessary to repeat the depression procedure another 59 times. For this reason, it is not practicable to provide for continuous correction from the minutes data to the hours data, i.e. to provide for a carry into the hours data register when a value of 59 in the minutes data register is exceeded. It is therefore generally necessary to provide two pushbutton switches for correction of such a digital display, one of which selects the digit or digits to be corrected, and the other being a correction switch which is repetitively depressed to perform the actual correction. It will be apparent that such a correction procedure is rather inconvenient and complex, by comparison with the analog timepiece correction method using a rotatable crown.
In electronic timepieces of the prior art which have combined analog and digital displays, it has been usual to provide separate correction means for the analog and digital displays which are basically as described in the preceding paragraph, i.e. a rotatable external operating member such as a crown is used to correct the analog display, while at least two pushbutton switches are used to correct the digital display. Thus, the time correction procedure is extremely complex and inconvenient in such a timepiece.
It is therefore highly desirable that means be provided in an electronic timepiece having both analog and digital time displays, whereby both of said analog and digital displays can be corrected in a simple and rapid manner, and whereby the number of operating members provided externally to perform such correction can be minimized.